The advances today in research and clinical medicine have demonstrated the feasibility of restoring the sensation of hearing to the hundreds of thousands of people in this country with profound deafness. Vital to the ultimate success of a cochlear prosthesis is the functional integrity of the neurons of the spiral ganglion and central auditory nuclei which must process and relay the electrical signals. Further understanding of the degenerative process that occurs in these structures after damage to the peripheral organ is, therefore, of fundamental importance. Towards this goal, the proposed research will: 1) systematically study the response of the spiral ganglion to various cochlear pathologies and correlate these changes with those occurring in the central auditory nuclei; and 2) determine if degenerative processes can be prevented or reversed by reintroduction of bioelectrical activity through the use of peripheral electrical stimulation. The avian auditory system, because of its relative simplicity and consistent response to cochlear damage, will be used for study. The pathologies to be investigated include cochlear removal, noise trauma, and aminoglycoside toxicity. The dependent measures will include cell loss, cell size changes (Nissl stains), and various metabolic parameters (amino acid incorporation, glucose metabolism, succinate dehydrogenase levels). These measures will allow the temporal pattern of neuronal degeneration to be more clearly defined. The effect that maturation of the auditory system has on its response to cochlear damage will be investigated by using different age groups of animals (neonate, mature adult, old adult). It is anticipated that this research will provide insights into the pattern and causes of degeneration of auditory neurons following severe injury to the cochlea and, thereby, provide a framework in which to study interventions intended to prevent peripheral and central nervous system atrophy.